Measuring and testing – Fluid pressure gauge – Vibration type
Patent
1998-10-28
2000-07-25
Oen, William
Measuring and testing
Fluid pressure gauge
Vibration type
G01L 1100
Patent
active
060924233
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to rate sensors of the kind including a resiliently-mounted element, an actuator that vibrates the element in a first plane, and a displacement sensor responsive to displacement of the vibrating element in a sensing direction normal to the first plane caused by rotation of the sensor about an axis in the plane and at right angles to the sensing direction.
BACKGROUND OF THE INVENTION
Vibrating element rate sensors, such as tuning fork gyros, have an element driven to vibrate in one plane. When the sensor is subject to rotation about an axis parallel to the vibration plane, a force is produced on the vibrating element orthogonal to the axis of rotation and the plane of vibration. This tends to cause deflection of the element, which is sensed by a suitable sensor, such as a capacitive pick-off.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved rate sensor.
According to one aspect of the present invention there is provided a rate sensor of the above-specified kind, characterized in that the displacement sensor includes a tunnel pick-off having a first part located on the vibrating element and a second part separate from the vibrating element, one part including a spike and the other part including a surface closely spaced from the tip of the spike.
The spike is preferably mounted on the vibrating element, the surface being on the second part. The tunnel pick-off may include two spikes, the surface having a recess located above one of the spikes, the output of the spike located beneath the recess being utilized to provide an output representative of vibration of the element. The sensor may include an actuator for maintaining constant average separation between the first part and the second part of the pick-off. The sensor may include an actuator so that the first and second parts can be displaced relative to one another from a position prior to use in which each spike is protected. The surface may have a recess positioned above each spike prior to use. The vibrating element is preferably a plate machined from a silicon substrate, the substrate supporting the second part of the tunnel pick-off. The actuator that vibrates the element in the first plane is preferably an electrostatic actuator. The vibrating element may have two flexure arms, the vibrating element being tuned by removing material from a surface of the arms.
According to another aspect of the present invention there is provided a two-axis inertial rate sensor system including four pairs of rate sensors according to the above one aspect of the invention, characterized in that the rate sensors in each pair are mirror images of one another.
Other aspects of the present invention will become apparent from the following description, by way of example, of a two-axis inertial rate sensor system, including sensors according to the present invention, with reference to the accompanying drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of the sensor;
FIGS. 2A and 2B are sectional side elevation views, to an enlarged scale, of the pick-off assembly along the line II--II in FIG. 1, showing the assembly at a rest and operational state respectively;
FIG. 3 is a sectional side elevation, to an enlarged scale, showing a part of the vibrating element along line III--III of FIG. 1;
FIG. 4 is a plan view of the system; and
FIG. 5 is a plan view of a sensor with alternative actuators.
DETAILED DESCRIPTION OF THE DRAWINGS
With reference first to FIGS. 1 to 3, the sensor includes a silicon wafer substrate 1 of rectangular shape having a tine 2. The tine 2 is formed integrally from the wafer by using microengineering techniques, such as photolithography or micromachining, to cut an aperture 3 of inverted U shape. The tine 2 is located in the lower half of the wafer 1, the aperture 3 extending around three sides of the tine. A second aperture 4 is cut laterally across the middle of the bottom of the tine 2 to leave two vertical flexure beams 5 and 6 pr
REFERENCES:
patent: 4267731 (1981-05-01), Jacobson
patent: 5485053 (1996-01-01), Baz
patent: 5922212 (1999-07-01), Kano et al.
Oen William
Smiths Industries Public Limited Company
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